The etch rates of gaseous HCI on AIN and GaN in H-2 ambient in a MOVBE reactor have been studied. For AIN, etching by HCI in H-2 and N-2 is compared. When etching GaN in hydrogen by HCI, a dependency of etch rate on temperature was found and the activation energy was determined. We propose a two-step reaction in which the first step, the decomposition of GaN, is the limiting one. The second step consists of a reaction of Ga with HCI to form volatile GaCI. We noticed that the decomposition step is enhanced with increased hydrogen partial pressure. Further, we observed that a coverage of the surface with Ga enhances the decomposition rate. By using a pulsed supply of HCI into the reactor a Ga-rich surface was maintained and the etch rate enhanced up to a temperature of 830 degrees C. (C) 2013 Elsevier BM. All rights reserved,